1. Field of the Invention
The present invention generally relates to an advection fan and an impeller thereof and, more particularly, to an advection fan that draws and expels air in a radial direction, as well as an impeller thereof
2. Description of the Related Art
Conventional cooling fans include axial-flow fans and blower fans. The axial-flow fan has an axial air inlet and an axial air outlet opposite to the axial air inlet. Air can be drawn via the axial air inlet and then expelled via the axial air outlet. The blower fan has an axial air inlet in the axial direction and a radial air outlet in the radial direction of the fan. Air can be drawn via the axial air inlet and then expelled via the radial air outlet for cooling purposes.
However, since the axial-flow fan expels air only in the axial direction rather than in the radial direction, the axial-flow fan must be mounted on the top of an electronic device to be cooled, such as a Central Processing Unit (CPU) of a computer. As a result, the height of the electronic device cannot be reduced. In addition, since the blower fan draws air via the axial air inlet (draws air in the axial direction) and expels air via the radial air outlet (expels air in the radial direction), the blower fan cannot be applied to electronic devices that draw air in the radial direction, such as a handset or a Personal Digital Assistant (PDA).
In light of the problems, other advection fans capable of drawing and expelling air in the radial direction were developed to fit the needs, as they can be applied to the electronic devices that draw air in the radial direction. However, since modern electronic devices usually have a miniature design, the height of the impeller of the advection fan must be efficiently reduced without affecting the air-driving capacity of the advection fan. The impeller of the advection fan is integrally formed of plastic material or integrally formed by punching of metal material. When the impeller is integrally formed into a predetermined shape by plastic material, the impeller may have a smaller structural strength if the impeller has a smaller thickness. Although the thin impeller may have a larger structural strength when it is integrally formed by punching of metal material, the costs are increased if a larger amount of metal material is used. The weight of the impeller is also increased when the motor drives the impeller to rotate, affecting the overall operation efficiency of the motor.
Referring to FIG. 1, Taiwan Patent No. M350746 discloses a thin rotor 8 having a thin impeller that is a common impeller design currently available in the market. The rotor 8 has a metal housing 81, a shaft 82 coupled to a center of the housing 81, and a metal blade frame 83 extending outwards from the periphery of the housing 81 in the radial direction. The metal blade frame 83 is coupled with a plastic blade portion 84. In this arrangement, although the rotor 8 is thin, the rotor 8 may still have a larger structural strength, since the primary structures of the rotor 8 are the metal housing 81 and the metal blade frame 83. Furthermore, the rotor 8 also has a lower cost, since the structure that is used to drive air is made of plastic (the plastic blade portion 84), allowing the rotor 8 to be manufactured into a thin shape with improved structural strength. However, the rotor 8 still has some problems stated below.
First, the rotor 8 is only suitable for use in a blower fan because the air-driving faces of the plastic blade portion 84 face two opposite axial directions of the shaft 82. Thus, although the rotor 8 may have a thin form with improved structural strength, the rotor 8 is not suitable for use in an advection fan.
Second, the rotor 8 has a hub 85 that blocks the airflows that are driven by the plastic blade portion 84. The part of the rotor 8 between the center of the housing 81 (where the shaft 82 is coupled) and the outer periphery of the metal blade frame 83 (where the plastic blade portion 84 is coupled) is not in a flat form. Namely, the structure of the rotor 8 where the housing 81 connects to the metal blade frame 83 forms the hub 85 having a protrusion form. Moreover, the top edge 841 of the plastic blade portion 84 is also not higher than the top face of the hub 85 in an axial direction. As a result, the hub 85 will block the airflows driven by the plastic blade portion 84 when the rotor 8 is installed in an advection fan for driving air into and out of the advection fan in the radial direction, affecting the performance of the rotor 8.
First, the rotor 8 is only suitable for use in a blower fan, because the air-driving faces of the plastic blade portion 84 face two opposite axial directions of the shaft 82. Thus, although the rotor 8 may have a thin form with improved structural strength, the rotor 8 is not suitable for use in an advection fan.
In the above structure, since the blades 922 are formed on the outer circumferential face of the hub 921 and since the top edge of each blade 922 is aligned with the top face of the hub 921, the hub 921 will block the airflows and therefore limit the outputted air volume of the advection fan. Thus, the cooling efficiency of the advection fan is significantly affected. Turbulence and noise also result easily.
In summary, since the hub 85/921 of the thin impeller tends to occupy a larger space in the air channel of the fan whether the impeller is one used in the blower fan or one used in the modern advection fan, the air-driving ability of the fan will be limited. As a result, satisfactory cooling effect is not provided. In light of this, it is necessary to improve the conventional advection fan.